(Phys.org)—Researchers have demonstrated a new way to enhance the emission of single photons by using "hyperbolic metamaterials," a step toward creating devices in work aimed at developing quantum computers and communications ...

(Phys.org)—Future computers are expected to use the laws of quantum physics to accomplish certain tasks in the blink of an eye that require decades for present-day computers. Physicists at the Max Planck Institute of Quantum ...

The storage of light-encoded messages on film and compact disks and as holograms is ubiquitous---grocery scanners, Netflix disks, credit-card images are just a few examples. And now light signals can be stored as patterns ...

Putting a hole in the center of the donut—a mid-nineteenth-century invention—allows the deep-fried pastry to cook evenly, inside and out. As it turns out, the hole in the center of the donut also holds answers for a type ...

(Phys.org) -- German scientists have demonstrated a method of heralding entanglement between distant stationary quantum systems without destroying this particular state. The experimental set-up paves the way towards quantum ...

(PhysOrg.com) -- "Liquid state Nuclear Magnetic Resonance (NMR) has been successful for quantum information processing, Osama Moussa tells PhysOrg.com. However, there are some questions about scalability and other ...

(Phys.org) -- Credit cards which are completely fraud-proof and passports which cannot be forged: quantum physics could make both of these possible. This is explained by the fact that the quantum mechanical state of a particle, ...

Quantum information

In quantum mechanics, quantum information is physical information that is held in the "state" of a quantum system. The most popular unit of quantum information is the qubit, a two-level quantum system. However, unlike classical digital states (which are discrete), a two-state quantum system can actually be in a superposition of the two states at any given time.

Quantum information differs from classical information in several respects, among which we note the following:

However, despite this, the amount of information that can be retrieved in a single qubit is equal to one bit. It is in the processing of information (quantum computation) that a difference occurs.

The ability to manipulate quantum information enables us to perform tasks that would be unachievable in a classical context, such as unconditionally secure transmission of information. Quantum information processing is the most general field that is concerned with quantum information. There are certain tasks which classical computers cannot perform "efficiently" (that is, in polynomial time) according to any known algorithm. However, a quantum computer can compute the answer to some of these problems in polynomial time; one well-known example of this is Shor's factoring algorithm. Other algorithms can speed up a task less dramatically - for example, Grover's search algorithm which gives a quadratic speed-up over the best possible classical algorithm.

Quantum information, and changes in quantum information, can be quantitatively measured by using an analogue of Shannon entropy. Given a statistical ensemble of quantum mechanical systems with the density matrix S, it is given by

Many of the same entropy measures in classical information theory can also be generalized to the quantum case, such as the conditional quantum entropy.